How to embed a LaTeX equation inside Inkscape

Recent versions of Inkscape (since 0.48?) have built-in support
for including a LaTeX formula inside a drawing. It is on the menu bar: Extensions->Render->LaTeX Formula.

This menu might be hidden if Inkscape cannot find these helper programs: latex, dvips, pstoedit. On Ubuntu, you can install these programs with the command,

sudo apt-get install texlive pstoedit

Alternatively, you can use the textext extension. It is similar to the build-in LaTeX support,
but has a slightly more polished input interface.

How to embed an Inkscape drawing inside a LaTeX document

From the menu : File -> Save a Copy.
On the lower right corner, choose file type "Encapsulated PostScript (*.eps)"

In your LaTeX file, use "\includegraphics{filename.eps}".
For a tutorial on how to use the EPS file inside LaTeX,
search on Google: latex import graphics.

How to turn an Inkscape drawing into an editable LaTeX document

From version 0.48, Inkscape has a special PDF+LaTeX output option.
All lines and shapes are saved into a PDF file, while all texts are saved
into a LaTeX file. Compiling this LaTeX will give you back the whole drawing.

This method allows you to use LaTeX equations.
You can also export EPS+LaTeX or PS+LaTeX.
More details is here: SVG in LaTeX (CTAN).

Lyx

LyX provides a GUI frontend for creating and editing a LaTeX document. If you want to use PDF+LaTeX from Lyx, you have to put this in your Latex preable (in Lyx, menu "document" -> "preferences" -> "latex preamble"):